genes from the original bacteria endosymbiont migrated to the nucleus

what eukaryotic organisms don't contain mitochondria?

single-celled eukaryotic organisms found in oxygen-free environments

many eukaryotes that lack mitochondria contain small organelles called:

hydrogenosomes that generate ATP by anaerobic processes. hydrogenosomes are basically highly altered mitochondria adapted to life in oxygen-poor environments

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other anaerobic eukaryotes contain smaller organelles called:

mitoses that also appear to be remnant mitochondria; only has genes needed for assembling the clusters of iron and sulfur found in many proteins

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nuclear genes in Eukarya resemble those of Archaea because:

primoridal eukaryotic host cell was closely related to Archaea

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what are two hypotheses for the origin of the eukaryotic cell?

1. eukaryotic cells evolved from an ancestral archaeon and only later incorporated the proteobacterial cell that became a mitochondrion2. eukaryotic cells evolved from a symbiosis between an archaeon and a proteobacterium. the proteobacterium became a mitochondrion.